The topic of “Further Enhancements to LTE Time Division Duplex (TDD) for Downlink-Uplink (DL-UL) Interference Management and Traffic Adaptation” (eIMTA) has been agreed as a study item in 3rd Generation Partnership Project (3GPP) release 11 and as a work item in 3GPP release 12. Thus, reconfiguration mechanism and interference mitigation scheme have been topics under discussion for devices having “Enhanced Interference Mitigation & Traffic Adaptation” (eIMTA) capabilities. For an eIMTA network apparatus such as a base station, a relay station, or a user equipment (UE), the UL-DL subframe configuration can be modified once for as short as every 10 milliseconds. Otherwise, without eIMTA, the UL-DL subframe configuration of a network apparatus can only be changed every modification period of the system information. Performance evaluation of various deployment scenarios has been conducted by both 3GPP RAN 1 and RAN 4 working groups. It has been shown that the average cell throughput of a Time Division Duplex (TDD) Long Term Evolution (LTE) communication system can be improved to a large extent by adopting eIMTA. Relay stations have been introduced in 3GPP release 10 as a means for coverage extension and/or throughput enhancement. It can be envisioned that relay stations be enhanced with the capability of eIMTA in future releases.
As TDD is utilized in eIMTA, TDD offers flexible deployments without requiring a pair of spectrum resources. Currently, LTE TDD allows for asymmetric DL-UL allocations by providing a predefined set of semi-statistically configured UL-DL configurations that is illustrated in FIG. 1. According to FIG. 1, for the case of a current LTE communication system for example, there could be seven different UL-DL configurations 101 which define whether a subframe of a radio frame is an uplink subframe, a downlink subframe, or a special subframe. These configurations can provide between 40% and 90% DL subframes. For transmissions between a macro base station and a relay node, the base station would be able to configure each subframe of a radio frame as a downlink subframe, an uplink subframe, or as a special subframe by selecting one of configurations 0˜7 as shown in FIG. 1, and the configuration would be communicated throughout a cell via a system information block (SIB) such as SIB 1.
Since the semi-static configuration may not match the instantaneous traffic condition, currently a UL-DL configuration could be reconfigured based on a system information change procedure. Additional mechanisms could include means such as dynamic reconfiguration of subframes to a different UL-DL configuration. In comparison to the system information change procedure, a dynamic mechanism may allow a much shorter period to reconfigure of the current TDD DL-UL configuration. Such idea has been termed eIMTA in 3GPP. Evaluations in the corresponding study items have revealed significant performance benefits by allowing dynamic TDD UL-DL reconfigurations based on traffic adaptations in small cells according to “Further enhancements to LTE TDD for DL-UL interference management and traffic adaptation,” 3GPP TR 36.828, V11.0.0, 2012-06. Also, dynamic signaling mechanisms would usually outperform a system that uses a system information change procedure. Further details related to LTE TDD frame structure and UL-DL configurations are described in “Physical Channels and Modulation”, 3GPP TS 36.211, V1.0.0, 2012-09, which is incorporated by reference. The aforementioned TS 36.211 reference also describes the current implementation of MBSFN, frame structure type 2, and control format indicator channel in further details.
In a legacy LTE TDD system, the DL Hybrid Automatic Repeat Request (HARQ) is defined separately and independently for each UL-DL configuration. Dynamic changes of UL-DL configurations in a TDD eIMTA system may therefore cause a DL HARQ timing discontinuity. Specific details regarding the current UL HARQ and DL HARQ operations are recorded in “Physical Layer Procedures”, 3GPP TS 36.213, V11.0.0, 2012 September which is incorporated by reference. According to Draft Report of 3GPP TSG RAN WG1 #74bis, it has been agreed by 3GPP RAN WG1 that a DL HARQ reference configuration is selected from UL/DL configuration {2, 4, 5} and is configured by higher layer signaling.
Subframes that are configured as UL in DL HARQ reference configuration cannot be changed to a DL subframe. Similarly, as an UL HARQ reference configuration is selected and follows the UL-DL configuration as indicated in System Information Block 1 (SIB1), a subframe that is configured as DL in UL HARQ reference configuration by SIB 1 cannot be dynamically changed to an UL subframe. Therefore, in order to implement a dynamic reconfiguration which is to change the current UL-DL configuration disregarding system information modification boundaries, valid UL-DL configurations 203 that corresponds to a UL HARQ reference configuration 201 and a DL HARQ reference configuration 202 could be obtained and summarized in FIG. 2. The current implementation UL-DL configuration for eIMTA is further described in “Physical Layer Procedures”, 3GPP TS 36.213, V11.0.0, 2012 September which is incorporated by reference.
Relay stations are introduced in 3GPP release 10 as a means for coverage extension and/or throughput enhancement. FIG. 3 illustrates an exemplary LTE communication system that includes at least but not limited to a base station 301 communicating with a user equipment (UE) 303 through a relay node 302. The base station 301 may transmit to the relay node 302 through a downlink channel, and the relay node 302 may transmit to the UE 303 through a downlink channel on the same frequency but in a different time slot. The downlink transmission between base station 301 and the relay node 302 cannot occur the same time as the transmission between the relay node 302 and the UE 303 since both downlink transmissions share the same frequency spectrum. Therefore, for in band relays, transmission gaps where the relay stations stops transmitting to or receiving from UE have to be configured on a regular basis to allow backhaul communication between the relay and the macro base station. Relay stations cannot utilize TDD configuration 0 and 5 because of the deficient number of DL and UL subframes. For the remaining 5 configurations, configurations {1, 2, 3, 4, 6}, the backhaul subframe configuration defines the DL-UL configuration for backhaul communication between the relay and the macro base station.
The conventional subframe configurations for a backhaul link between a base station and a relay node is defined as SubframeConfigurationTDD in FIG. 4. The current implementation of SubframeConfigurationTDD as shown in FIG. 4 is further described in “Physical Layer for Relaying Operation”, 3GPP TS 36.216, V11.0.0, 2012 September which is incorporated by reference. The aforementioned TS 36.216 reference also describes related implementations of physical channels and modulation in detail. For FIG. 4, as mentioned previously, configurations 0 and 5 from FIG. 1 have been disregarded because of insufficient uplink or downlink subframes. The eNB-RN UL-DL configuration 402 lists remaining possible TDD configurations to be used between a base station 301 and a relay node 302. For each eNB-RN UL-DL configuration, one or multiple possible TDD subframe configurations could be used between a base station 301 and a relay node 302 as listed in SubframeConfigurationTDD 401. In general, the SubframeConfiguration TDD is a label that describes one or more different configurations of subframes for each UL-DL configuration for transmission between a base station and a relay node and can be configured for higher level signaling.
However, to incorporate the operation of eIMTA, the conventional transmission gaps used by a relay station may hinder the operation of eIMTA. Consequently, eIMITA cannot be directly applied on a relay node.